Windmills and the like are known to those familiar with the prior art. Such devices have the common feature of presenting impeller structures to air currents for the purpose of deriving a rotational motion therefrom. The rotational motion may be put to several uses such as the generation of electrical energy or the direct powering of a rotary machine, for example, a pump.
Typical prior art windmills have a plurality of blades positioned around a shaft, the blades either being secured directly to the shaft or to radial struts extending from the shaft. To generate great amounts of power, such devices have required complex structures to support the full expanse of the blades and/or radial struts. Also, multiple stage devices of the type described require a duplication of elements for each stage, the radial struts, for example. Further, the use of radial struts has the effect of impeding the very air current from which it is desired to derive power.